The present invention relates to food preparation ovens, and in particular, to combination convection and steam ovens.
Combination ovens provide the ability to cook foods using steam, hot air convection or both steam and convection. A motor driven fan is ordinarily used to circulate air within a cooking chamber past electrical heating elements or gas heat exchange tubes. To produce steam within the cooking chamber, a water line feeds water into the cooking chamber near the heating elements to vaporize the water.
Combination ovens typically feed water to the center of the fan so that the water is drawn through the fan. Contact of the water with the fan blades separates the water into small droplets providing a larger overall surface area which can be vaporized more efficiently. To further improve thermal efficiency, some combination ovens include an atomization element at the hub of the fan which is rotated by the motor. The atomization element acts to initially break up the water before it is further reduced by the fan blades. The atomization process produces a fine mist of water surrounding the heating elements.
It is desirable to control the level of humidity during the cooking process. For example, low humidity may be desired when cooking by radiant heating or convection without steam to form a crust on the outside of certain foods, such as pastries, breads and meats. However, if the food has a high water content, the excess moisture can evaporate into the cooking chamber and prevent the formation of crust. This can also affect the cooking time and texture of food cooked with steam. Moreover, when cooking with steam it may also be desirable to quickly evacuate the moisture from the cooking chamber in a controlled manner so that a second food can be cooking using a radiant or convective process and to reduce the volume of steam escaping from the cooking chamber when the oven door is opened. This is particularly useful in the commercial food preparation industry.
It is also important to be able to quickly vent the cooking chamber to alleviate certain low or high-pressure conditions within the cooking chamber that can result, for example, from frozen food being placed in a hot cooking chamber or when the oven door is closed rapidly. The cooking chamber is ordinarily vented through a valve operated chimney or vent. While this relieves the pressure imbalance, it can also cause significant temperature and humidity losses due to the interior of the cooking chamber being in direct communication with the outside air, which adversely effect the efficiency of the oven.
Accordingly, a combination steam and convection oven is desired that provides improved venting and humidity control.